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Topic: How to check your servo resolution? (Read 3291 times) previous topic - next topic

Soffer

May 23, 2012, 09:44 am Last Edit: May 23, 2012, 10:06 am by Soffer Reason: 1
Hey guys.
In trying to get my servo to move more delicately and so I've been trying to get it to to respond to microseconds.
It does, but in an accumulative fashion: I mean that not every microsecond pushes it a bit and the same "steps" of movements remain.
I guess this is due to the gears, right?
If so - my question than is how can I tell what is the resolution of my servo (Power HD 6001HB, and no, the manufacturer does not provide this info) - and more importantly, how can I create/get a servo that will respond in a more precise manner to the microsecond command?
Thanks.


DuaneB

Yawn.

Put a long stick on the end of the servo, 10cm would be fine. Measure how much it moves for different signals. Work out the angles.

Digital servos are more expensive and more precise.

Duane B

rcarduino.blogspot.com
Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

Soffer

Hey Duane, thanks.
Seems weird that you buy a servo and than use a stick to measure its resolution.
It's like buying TV and using a magnifying glass to count the pixels.

What about the other issues I've raised? Any thoughts?

zoomkat

You can make a seup like below using a bamboo skewer so you can detect incremental movements of the servo. I found that a standard servo is capable of ~426 discrete movements in its ~190 deg rotation range. Servos have an internal dead band which can limit resolution. I found that ~5us is pretty mich the lower us resolution limit.

Google forum search: Use Google Advanced Search and use Http://forum.arduino.cc/index in the "site or domain:" box.

Soffer


You can make a seup like below using a bamboo skewer so you can detect incremental movements of the servo. I found that a standard servo is capable of ~426 discrete movements in its ~190 deg rotation range. Servos have an internal dead band which can limit resolution. I found that ~5us is pretty mich the lower us resolution limit.



zoomkat, is there a way to know this beforehand? Is there a way to increase servo resolution?

dxw00d

I would think the resolution would be limited by the relatively small pot used by the servo to determine its position.

Soffer


I would think the resolution would be limited by the relatively small pot used by the servo to determine its position.

As I understand dxw00d, it is limited by the gears, but my question reamins: Is there no way to know this from the spec sheet?
Is there no way to better the resolution?

DuaneB

Better resolution is available through a bell crank or similar mechanical arrangement that swaps range for resolution.

If you have a quality servo it may have a spec sheet, a lower quality servo will not or may not comply with one if it does.

Duane B

rcarduino.blogspot.com
Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

Soffer


Better resolution is available through a bell crank or similar mechanical arrangement that swaps range for resolution.

Duane B



Any chance of you being more specific about this?

AWOL

Check any R/C site for details of cranks.

Why don't you tell us what you're trying to do?
Maybe there's a better solution.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Erni

#11
May 24, 2012, 11:35 pm Last Edit: May 24, 2012, 11:37 pm by Erni Reason: 1
If you use a digital servo like Hitec, you can program the deadband to 0 uS
Another example:
The datasheet for this Hyperion Atlas servo shows programmebly deadband 0 uS to 16 uS (2 uS default)

Try a search on http://www.rcgroups.com/

Soffer


Check any R/C site for details of cranks.

Why don't you tell us what you're trying to do?
Maybe there's a better solution.


AWOL, I've been building my own recordable Follow Focus system. 
(You can get some more info on a modest blog I started: http://adisoffer.tumblr.com/,
although I've jsut began passing the info there)
Anyway' the thing is built around a servo that gently rotates the focus ring of a lens, and that is why I'm trying to get it to be as smooth as possible.

Would appreciate your thoughts!
:)

AWOL

How are you doing the drive coupling?
I was imagining something like the split-band drive around the focus ring.
Split-bands were used on old HDDs which had stepper motors to move the heads before voice coils became common.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Soffer


How are you doing the drive coupling?
I was imagining something like the split-band drive around the focus ring.
Split-bands were used on old HDDs which had stepper motors to move the heads before voice coils became common.


Whoops! Have no idea what you're talking about...  :smiley-eek:
Just to make sure I'm explaining my self correctly:
The setup is very much like the "Knob" sketc, plus added power to the servo (using Vregulator and decoupling capacitors).
The code was modified to fit certain needs (recording and playing back...).
The servo has a cog wheel attached to it, and this in turn fits to a ring that wraps around any lens I use.

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